—_______ My father bought a new computer for me.
—Really?
A:What's wrong?
B:Guess what?
C:Hurry up!
D:Nice idea!
一个质量为10kg的物体,以10m/s的速度做直线运动,受到一个反方向的作用力F,经过4s,速度变为反向2m/s.这个力是多大?
当你想询问你的橡皮在哪里时,你应该说: